1 Field of the Invention
The present invention relates to a chain saw cutting tool and, in particular, to a non-driving guide pulley or sprocket on a chain saw cutting tool.
2 Description of Related Art
Chain saw guide bars are commonly provided with a thin nose sprocket for carrying the saw chain around the nose of the guide bar. The nose sprocket is inserted between two side plates of the laminated or solid guide bar and has a roller bearing to carry the loads from chain tension and cutting. Lateral forces are usually small, and leakage of chain lubricating oil onto the sprocket sides is usually enough to avoid friction problems on the sprocket sides.
In severe service such as in tree harvester machines, however, the nose sprocket runs very fast and with higher loads. It is common that the sprocket becomes slightly deformed from overheating, which causes it to rub against the side plates of the guide bar. This rubbing may lead to excessive wear, fretting or seizure.
It has been previously suggested that lubricating oil should be supplied to the central region of the sprocket through channels such as disclosed in U.S. Pat. No. 3,044,506 and 3,279,508, or that the sprocket should be made with spiral grooves to catch and convey chain oil from the chain groove towards the sprocket center such as disclosed in U.S. Pat. No. 5,092,044. None of these solutions works well if the area of the sprocket being rubbed is at the lowest part of the sprocket teeth, which is very common.